Volume Ten - Pre-Victorian to the Present Day - Even more aspects - Investigation into the Condition of the Ely River Subway 1991 . . .

The presence of Penarth Dock on the south bank of the river prevented the Engineer, Mr George T Sibbering, from adopting a straight alignment for the Subway.  A horizontal curve to the Subway on the south side of the river was required which subtended an angle of approximately 73 degrees and allowed the alignment to run parallel to Penarth Dock before emerging adjacent to the lock between the Basin and the Dock. 

The gradients adopted for the Subway beneath the north and south banks of the river were 1:9 and 1:7 respectively and approximated to the ground profile of the two banks. The two gradients were aligned beneath the river with a vertical curve.

The Subway was constructed to a circular cross section and lined with cast iron rings providing an internal diameter of 2.69m.  A 1.83m wide concrete pavement in the invert of the Subway gave a headroom clearance of 2.29m.  Each 457mm wide cast iron ring section was formed from seven segments with a key block at the crown and bolted together via flanges on each edge of the segment.

The rings themselves were bolted together in a similar manner The abutting edges of adjacent segments and rings would either have been machine faced or sealed with lead caulking in order to prevent water ingress.  The annulus between the outside of the rings and the surrounding ground was also grouted as a means to stem water ingress into the Subway.

• 23rd August 1897 - Commencement of Subway in open cut on the north bank of the Ely River.

The geology of the area would have been well known from the excavations needed to construct Penarth Dock and Mr Sibbering also undertook a site investigation, including boreholes, to provide additional information on the geology.